Counter-terrorism officials meeting in Vienna say it will take time for the international community to fight terrorism more effectively, and even then, terrorists will likely still be able to carry out attacks like the ones Thursday in Madrid.

Officials from the United Nations and the Organization for Security and Cooperation in Europe concluded a two-day meeting Friday, determined to increase joint efforts to fight terrorism following the massacre in Madrid.

Spain's ambassador to the United Nations is the chairman of the Security Council's Counter-Terrorism Committee. Ambassador Inocencio Arias said Friday there are limits to what can be done to fight terrorist groups.

"Even with a lot of international cooperation, you can never be sure that you are going to have no terrorism, because terrorists keep trying all year, and then you prevent them from doing something 49 times, and then the 50th time, they succeed," the ambassador said.

Still, Mr. Arias said, there are steps that can be taken to weaken the base for terrorists.

"If the terrorists don't find shelter in other countries, if terrorists are extradited, if terrorists cannot do any money laundering, the possibility of them acting becomes not one-tenth, but one-hundredth," he said.

Ambassador Arias said international organizations are working together to avoid duplication and improve their exchange of information, so they can stop terrorist plots more efficiently.

At the meeting this week, delegates also encouraged governments to tighten airport security and passport controls to ensure potential terrorists are stopped when they try to travel.